Relationships between birthweight and plasma thyroxine, triiodothyronine and iodide concentration in lambs.

In crossbred lambs, during the first hours of postnatal life, plasma thyroxine and triiodothyronine concentrations were similar in animals spontaneously born on days 143, 145 or 147 of gestation. However, during the 72 h following delivery, a positive linear relationship was observed between birthweight and plasma T4 or T3 concentrations among the lambs born on day 145. Within 6 h after birth, plasma iodide concentrations reached their highest values, subsequent to the ingestion of iodine from the maternal milk.